1. Field of the Invention
The invention relates to an electrode body that, when used in a battery, allows increasing the discharge capacity of the battery beyond that of a conventional battery, while reducing voltage drops, and relates to a method for producing such an electrode body.
2. Description of Related Art
In secondary batteries, the decrement in chemical energy that accompanies a chemical reaction can be converted to electric energy, such that the battery can be discharged; also, electric energy can be converted to chemical energy and be charged in the battery by causing current to flow in a direction opposite to that during discharge. Among secondary batteries, secondary batteries typified by lithium secondary batteries exhibit high energy density, and hence are widely used as power sources in notebook personal computers, cell phones and the like.
A reaction represented by formula (I) below takes place in the negative electrode during discharge in a case where graphite (represented by C) is used as a negative electrode active material in a lithium secondary battery.LixC6→6C+xLi++xe−(I) (in formula (I), 0<x<1)The electrons generated in the reaction of formula (I) pass through an external circuit, perform work at an external load, and arrive to the positive electrode. The lithium ions (Li+) that are generated in formula (I) move by electro-osmosis from the negative electrode towards the positive electrode through an electrolyte that is sandwiched between the negative electrode and the positive electrode.
The reaction represented by formula (II) below takes place in the positive electrode during discharge, in a case where lithium cobalt oxide (Li1−xCoO2) is used as the positive electrode active material.Li1−xCoO2+xLi++xe−→LiCoO2(II) (in formula (II), 0<x<1)During charging, reverse reactions to those of formula (I) and formula (II) take place in the negative electrode and the positive electrode, respectively, so that in the negative electrode, graphite into which lithium is incorporated (LixC6) is regenerated through graphite intercalation, and lithium cobalt oxide (Li1−CoO2) is regenerated in the positive electrode. Re-discharge is made possible thereby.
LiCoO2 that is used as a positive electrode active material in an all-solid-state lithium secondary battery has a strong tendency to exhibit c-axis orientation when made into a thin film, and hence exchange of lithium ions between the positive electrode active material and a solid electrolyte does not take place smoothly, and the output current of the all-solid-state lithium secondary battery decreases as a result. With a view to solving such a problem, Japanese Patent Application Publication No. 2012-099405 (JP 2012-099405 A) discloses a technology for tilting the c-axis in a lithium cobalt oxide crystal obliquely with respect to the normal of a substrate. This technology relies on a sintered compact that is provided with a conductive substrate and with an orientation layer that is formed through magnetic orientation, on at least one surface of the conductive substrate, wherein the orientation layer is made up of spherical particles of lithium cobalt oxide (LiCoO2), and the c-axis of the lithium cobalt oxide is oriented in a predetermined direction that is oblique, by a predetermined angle or more, with respect to the normal direction of the conductive substrate.